3-hydroxy-N-methylpyrrolidone and use as transdermal enhancer

ABSTRACT

The novel compound, 3-hydroxy-N-methylpyrrolidone, is effective as a transdermal enhancer for the absorption of drugs through the skin of humans and animals. The 3-hydroxy-N-methylpyrrolidone is prepared from delta-butyrolactone which is converted to methyl 2,4-dibromobutyrate, this intermediate is reacted with methylamine to form N-methyl-2,4-dibromobutyramide, this intermediate is converted to 3-bromo-N-methyl-2-pyrrolidone by ring closure, and the 3-bromo-N-methyl-2-pyrrolidone is reacted with an alkaline earth metal carbonate or alkaline metal carbonate to form 3-hydroxy-N-methyl-2-pyrrolidone.

This is a division of application Ser. No. 07/263,384 filed Oct. 27,1988, now U.S. Pat. No. 4,973,708, dated Nov. 27, 1990.

TECHNICAL FIELD

This invention relates to a new composition for drug delivery and moreparticularly relates to use of the compound3-hydroxy-N-methylpyrrolidone as a transdermal enhancer for theabsorption of drugs into humans and animals by absorption through theskin.

BACKGROUND ART

Transdermal absorption is currently one of the fastest growing methodsof drug delivery. Transdermal therapeutic systems are self-containeddosage forms that, when applied to intact skin, deliver drug(s) at acontrolled rate to the systemic circulation. Advantages of using thetransdermal route include: enhanced therapeutic efficacy, reduction inthe frequency of dosing, reduction of side effects due to optimizationof the blood-concentration versus time profile, increased patientcompliance due to elimination of multiple dosing schedules, bypassingthe hepatic "first-pass" metabolism, avoiding gastrointestinalincompatibilities and providing a predictable and extended duration ofactivity. However, the main function of the skin is to act as a barrierto entering compounds. As a consequence, transdermal therapy has so farbeen restricted to a limited number of drugs that possess the desirablephysiochemical properties for diffusion across the skin barrier. Oneeffective method of overcoming the barrier function of the skin is toinclude a penetration enhancer in the formulation of a transdermaltherapeutic system. See Barry, Brian W.: Dermatological Formulations:Percutaneous Absorption (Dekker, New York, 1983); Bronough et al,Percutaneous Absorption, Mechanisms-Methodology-Drug Delivery, (MarcelDekker, New York, N. Y. 1985); and Monkhouse et al, Transdermal drugdelivery-problems and promises. Drug Dev. Ind. Pharm., 14, 183-209(1988).

A penetration enhancer is a chemical compound that, when included in aformulation, temporarily increases the permeability of the skin to thedrug allowing more of the drug to be absorbed in a shorter period oftime. Several different types of penetration enhancers have beenreported such as dimethylsulfoxide, n-decyl methyl sulfoxide,N,N-dimethylacetamide, N,N-dimethylformamide,1-dodecylazacycloheptan-2-one (Azone), propylene glycol, ethanol,pyrrolidones such as N-methyl-2-pyrrolidone (NMP) and surfactants. SeeBronough et al, supra, and Stoughton et al, Azone: A New Non-toxicenhancer of percutaneous penetration. Drug Dev. Ind. Pharm., 9, 725-744(1983).

N-methyl-2-pyrrolidone is a versatile solvent which is miscible withwater, ethyl alcohol, ether, chloroform, benzene, ethyl acetate andcarbon disulfide. N-methylpyrrolidone has been widely used as a solventin industrial processes such as petroleum refining, GAF Corp.: "M-Pyrol(N-methyl-2-pyrrolidone) Handbook.", GAF Corp., New York, 1972. It iscurrently used as a solubilizing agent in topical and parenteralveterinary pharmaceuticals and is now under consideration for use inproducts intended for humans, Wells, D.A. et al: Disposition andMetabolism of Double-Labeled [³ H and ¹⁴ C] N-methyl-2-pyrrolidone inthe Rat. Drug Met. Disps., 16, 243-249 (1988). Animal and humanexperiments have shown very little irritation or sensitizaticnpotential. Ames type assays and chronic exposure studies have notrevealed any significant toxicity, Wells et al, Mutagenicity andCytotoxicity of N-methyl-2-pyrrolidone and 4-(methyl amino) ButanoicAcid in the Salmonella/microsome Assay. J. Appl. Tox., 8, 135-139(1988). N-methylpyrrolidone has also been shown to be an effectivepenetration enhancer. Barry et al, Optimization of Bioavailability ofTopical Steroids: Penetration Enhancers Under Occlusion. J. Inv. Derm.,82, 49-52 (1984); Akter et al, Absorption Through Human Skin ofIbuprofen and Flurbiprofen; Effect of Dose Variation, Deposited DrugFilms, Occlusion and the Penetration Enhancer N-methyl-2-pyrrolidone. J.Pharm. Pharmacol., 37, 27-37 (1984); Holegaard et al, Vehicle Effect onTopical Drug Delivery IV. Effect of N-methylpyrrolidone and Polar Lipidson Percutaneous Transport. Int. J. Pharm., 43, 233-240 (1988);Sugibayashi et al, Effect of Several Penetration Enhancers on thePercutaneous Absorption of Indomethacin in Hairless Rat. Chem. Pharm.Bull., 36, 1519-1528 (1988); Bennett et al, Optimization ofBioavailability of Topical Steroids: Non-Occluded penetration EnhancersUnder Thermodynamic Control. J. Pharm. Pharmacol., 37, 298-304 (1985);Sasaki et al, Enhancing Effect of Pyrrolidone Derivatives on TransdermalDrug Delivery. 1. Int. J. Pharm., 44, 15-24 (1988); Lee et al, Toxicityof N-methyl-2-pyrrolidone (NMP): Tetratogenic, Subchronic and Two-YearInhalation Studies, Fund. Appl. Tox., 9, 222-235 (1987).

There remains a need in the art of transdermal delivery for apenetration enhancer which is safe, effective, and provides advantagesnot known to penetration enhancers of the prior art.

DISCLOSURE OF THE INVENTION

It is accordingly one object of the present invention to provide a novelpenetration enhancer for use in transdermal drug delivery.

A further object of the present invention is to provide as a novelchemical compound, 3-hydroxy-N-methylpyrrolidone having advantageouscharacteristics as a penetration enhancer in transdermal deliverysystems.

A further object of the invention is to provide methods for preparationof the novel penetration enhancer, 3-hydroxy-N-methylpyrrolidone.

A still further object of the present invention is to providetransdermal delivery systems which contain as a safe and effectivepenetration enhancer, 3-hydroxy-N-methylpyrrolidone.

Other objects and advantages of the present invention will becomeapparent as the description thereof proceeds.

In satisfaction of the foregoing objects and advantages, there isprovided by this invention a novel penetration enhancing compound,3-hydroxy-N-methylpyrrolidone.

There is also provided by this invention a method for preparation of3-hydroxy-N-methylpyrrolidone which comprises conversion ofdelta-butyrolactone to methyl-2,4-dibromobutyrate, conversion of themethyl-2,4-dibromobutyrate to N-methyl-2,4-dibromobutyramide, ringclosure of the N-methyl-2,4-dibromobutyramide to form3-bromo-N-methyl-2-pyrrolidone, and conversion of the3-bromo-N-methyl-2-pyrrolidone to 3-hydroxy-N-methyl-2-pyrrolidone byreaction with alkali metal carbonate.

The present invention also provides transdermal compositions comprisingas the penetration enhancer, 3-hydroxy-N-methyl-2-pyrrolidone. Thepresent invention also provides a method for delivery of drugs throughthe human skin which comprises preparation of a transdermal drugdelivery system containing 3-hydroxy-N-methylpyrrolidone as apenetration enhancer, and applying the transdermal composition to thehuman skin.

BRIEF DESCRIPTION OF DRAWINGS

Reference is now made to the accompanying drawings wherein:

FIG. 1 is a graph showing a comparison of the percent penetration of ¹³¹I-labeled Clioquinol when delivered with 3-hydroxy-N-methylpyrrolidone,N-methylpyrrolidone, and without an enhancer;

FIG. 2 is a graph showing the percent penetration of ¹²⁵ I-labeledClioquinol using 3-hydroxy-N-methylpyrrolidone, N-methylpyrrolidone, andwithout an enhancer; and

FIG. 3 is an HPLC radiochromatogram of the 5-chloro-8-hydroxy-7-[¹³¹I]-iodoquinoline, the drug chosen to test the penetration enhancingcharacteristics of the compound of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

It has been discovered according to this invention that3-hydroxy-N-methylpyrrolidone, also known as3-hydroxy-N-methyl-2-pyrrolidone, is an effective penetration enhancerwhen used in transdermal drug delivery systems.3-hydroxy-N-methylpyrrolidone is a novel compound prepared according tomethods described herein. In general, the compound is a white solidhaving a melting point of 71°-72° C. and is of the following structuralformula: ##STR1##

This novel compound is prepared through a series of novel chemicalsteps, preferably using as the basic starting materialdelta-butyrolactone. In a preferred procedure, delta-butyrolactone isreacted with bromine in the presence of a bromide compound such asphosphorus tribromide and under an elevated temperature in the range of75°-125° C. In a preferred procedure, the bromide compound anddelta-butyrolactone are mixed with agitation and at an elevatedtemperature, liquid bromine is slowly added. The temperature may becontrolled in the preferred range by the rate of addition of the bromineand by external heating. Preferably the amount of bromine added to thebutyrolactone is in the molecular ratio of about 1:2. Bromine additionis stopped when HBr evolution becomes evident, after which the reactionmixture is cooled and combined with methanol. The resulting solution isthen saturated with HCl gas, the methanol is removed andmethyl-2,4-dibromobutyrate is removed as a pale yellow liquid.

In a second step of the reaction, the methyl-2,4-dibromobutyrate isreacted with methylamine in an aqueous solution at a temperature ofbelow ambient in order to form N-methyl-2,4-dibromobutyramide. Thenbutyramide is then recovered and purified to obtain the solidintermediate product.

The N-methyl-2,4-dibromobutyramide is then converted to3-bromo-N-methyl-2-pyrrolidone by reaction with alkali metal alkoxide toeffect ring closure. In this reaction, an alcoholic solution of theN-methyl2,4-dibromobutyramide is formed and freshly prepared alkalimetal alkoxide, preferably sodium ethoxide, is added drop-wise to themixture under an inert atmosphere. After the reaction is complete, themixture is filtered and the alcohol removed under reduced pressure. Thissolid intermediate is then purified to provide a yellow liquidintermediate product.

The recovered 3-bromo-N-methyl-2-pyrrolidone is then converted to the3-hydroxy-N-methyl-2-pyrrolidone of this invention by reaction with analkali metal or alkaline earth metal carbonate in a substantiallystoichiometric reaction and in an aqueous medium. Preferably thereactant is added to a solution of the 3-bromo-N-methyl-2-pyrrolidoneunder agitation and while heating in the range of 75°-125° C. After thereaction is complete, the 3-hydroxy-N-methylpyrrolidine white solidproduct is recovered and purified.

The following is a schematic showing this four-step reaction. ##STR2##

As pointed out above, a penetration enhancer is a chemical compoundwhich, when included in a transdermal formulation, affects the skin of ahuman by increasing permeability of the skin to allow more of a drug tobe absorbed in a shorter period of time. The penetration enhancer isnormally contained in a formulation, called a transdermal composition,in combination with the appropriate drug to be delivered and other knowncomponents of the formulation. According to this invention, it has beendiscovered that the 3- hydroxy-N-methylpyrrolidone provides unexpectedlyimproved effects as a penetration enhancer when incorporated into atransdermal formulation. As mentioned herein, N-methylpyrrolidone is aknown penetration enhancer. In studies leading to this invention usingthe prior art compound, N-methyl-2-pyrrolidone, it was discovered that amajor metabolite of N-methylpyrrolidone which is excreted in the urineis 3-hydroxy-N-methyl-2-pyrrolidone. The subsequent synthesis of thiscompound, and closer examination of physical properties of the compound,led to the present discovery that 3-hydroxy-N-methylpyrrolidonepossesses several advantages over similar compounds such asN-methylpyrrolidone as a penetration enhancer. Thus,3-hydroxy-N-methylpyrrolidone provides at least equal and often superiorenhancement of transdermal absorption while exposing the body to a lowermetabolic burden. Further, 3-hydroxy-N-methylpyrrolidone is a "softer"xenobiotic to the body because no energy will be expended in metabolicprocesses after the compound's absorption into the systemic circulation.Also, in view of the apparent safety of N-methylpyrrolidone, its majormetabolite, 3-hydroxy-N-methylpyrrolidone, would be expected to have aneven lower toxicity.

The 3-hydroxy-N-methylpyrrolidone of this invention may be used as thepenetration enhancer in any transdermal drug delivery system in which itis effective. It is considered that the 3-hydroxy-N-methylpyrrolidone iscompatible with all known drugs which are systematically active and canbe delivered in a transdermal system to be absorbed by the body surface.As is known, a transdermal delivery system comprises or reservoir forthe composition to be transferred including the drug of choice, thecarrier, and the penetration enhancer. In general, the reservoir will becontained between a backing member and a pressure-sensitive adhesivewhich enables the transdermal device to be applied to the skin.Transdermal delivery systems are well known in the art and described,for example, in U. S. Pat. Nos. 3,598,122, 3,797,494, and 4,230,105. Itis considered according to the present invention that the penetrationenhancer of this invention can be used in all such systems.

In practicing this invention one can employ any systemically active drugwhich will be absorbed by the body surface to which the transdermalbandage is applied, consistent with their known dosages and uses. Ofcourse, the amount of drug necessary to obtain the desired therapeuticeffect will vary depending on the particular drug used. Suitablesystemic drugs include, without limitation, Anti-microbial agents suchas penicillin and tetracycline; Sedatives and Hypnotics such aspentabarbital sodium and phenobarbital; Psychic Energizers such as3-(2-aminopropyl) indole acetate; tranquilizers such as reserpine,chloropromazine hydrochloride, and thiopropazate hydrochloride;Hormones; Antipyretics such as aspirin, salicylamide, and sodiumsalicylate; morphine and other narcotic analgesics; Antidiabetics, e.g.,insulin; Cardiovascular Agents, e.g., nitroglycerin, and cardiacglycosides such as digitoxin, Anti-spasmodics such as atropine, andmethscololamine bromide; Anti-malarials such as the 4-aminoquinolines;and Nutritional Agents such as vitamins, essential amino acids, andessential fats.

Further, topically active drugs consistent with their known dosages anduses can be administered. Suitable drugs include without limitation:Antiperspirants, e.g., aluminum chloride; Deodorants, e.g.,hexachlorophene, Astringents, e.g., tannic acid; Irritants, e.g., methylsalicylate, Keratolytics, e.g., benzoic acid; Antifungal Agents;Anti-inflammatory Agents; Anti-neoplastic Agents, And AntibacterialAgents.

The above and other drugs can be present in the reservoir alone or incombination form with pharmaceutical carriers. The pharmaceuticalcarriers acceptable for the purpose of this invention are the art knowncarriers that do not adversely affect the drug, the host, or thematerial comprising the drug delivery device. Suitable pharmaceuticalcarriers include sterile water; saline, dextrose; dextrose in water orsaline; condensation products of castor oil and ethylene oxide combiningabout 30 to about 35 moles of ethylene oxide per mole of castor oil;liquid glyceryl triester of a lower molecular weight fatty acid; loweralkanols; oils such as corn oil; peanut oil, sesame oil and the like,with emulsifiers such as mono-or di-glyceride of a fatty acid, or aphosphatide, e.g., lecithin, and the like; glycols; polyalkyleneglycols; aqueous media in the presence of a suspending agent, forexample, sodium carboxymethylcellulose; sodium alginate;poly(vinylpyrolidone); and the like, alone, or with suitable dispensingagents such as lecithin; polyoxyethylene stearate; and the like. Thecarrier may also contain adjuvants such as preserving, stabilizing,wetting, emulsifying agents and the like together with the penetrationenhancer of this invention.

The following examples are presented to illustrate the invention.However, it is not to be considered as limited thereto. In the examplesand through the specification, parts are by weight unless otherwiseindicated.

EXAMPLE 1 Synthesis of 3-hydroxy-N-methyl-2-Pyrrolidone

General. Melting points were determined on a Fisher-Johns melting pointapparatus and are uncorrected. H-NMR and C-NMR spectra were obtainedusing a Varian Gemini 200MHz or Varian XL-300 300 MHz spectrometer. Massspectra were run on a Kratos MS50 TA mass spectrometer with. aKratosDS90 data system. Infrared (IR) spectra were recorded on aPerkin-Elmer Ratio Recording spectrophotometer. Microanalysis wereperformed by Atlantic Microlab, Inc., Atlanta, Ga.

Reactions were routinely followed by thin layer chromatography (TLC)using Whatman K6F silica gel plates. Spots were visualized by exposureto iodine vapor or uv lamp (254 nm). Column chromatography was carriedout using silica gel (Davidson Chemical, Baltimore, Md.).

Materials. Delta-Butyrolactone (Aldrich, Cat. No. B10,360-8, lot 2710BK,99%), Bromine (J. T. Baker, Cat. No. 1-9760, lot 849381), Phosphoroustribromide (Aldrich, Cat. No. 25,653-6, lot 1413BM), methanol (Fisher,Cat. No. A-412, lot 854027), Methylamine, 40 wt % solution in water(Aldrich, Cat. No. M2,775-1, lot 03804CT), absolute ethanol (MidwestSolvents Company of Ill.), potassium carbonate (Aldrich, Cat. No.20,961-9, lot 04006BP, 99+%).

A. Methyl 2,4-dibromobutyrate. Phosphorous tribromide (2.0 ml, 5.7 gm,0.021 mole) was added to deltabutyrolactone (100.8 gm, 1.17 mole) andthe mixture was heated to 100° C. while stirring. Bromine (30 ml, 93.4gm, 0.59 mole) was slowly added dropwise beneath the surface of theliquid. The temperature was controlled at 110°-115° C. by the rate ofaddition of bromine and an oil bath. Additional PBr₃ (1.0 ml, 2.85 gm,0.011 mole) was added to the reaction vessel and bromine addition wasthen continued until HBr evolution was evident (approx. 25 ml, 80 gm,0.49 mole). The reaction mixture was stirred and cooled to roomtemperature and finally cooled in an ice bath. The mixture was combinedwith methanol (480 ml) and the resulting solution was saturated with HClgas. The solution was allowed to stand overnight at room temperatureafter which the methanol was removed under reduced pressure. The residuewas dissolved in ether, washed with 5% sodium bicarbonate solution,dried over magnesium sulfate and filtered. The solvent was removed andthe residue distilled under reduced pressure to yield a clear paleyellow liquid, 2 (216.4 gm, 71%); b.p. 80°-85° C. @ 2-3 mm of Hg,IR(neat) 1775, 1735, 1470 and 1380-1130 cm⁻¹ ; H-NMR (CDCl₃) δ 2.54 (q,2H, -CH₂ -CHBr-), 3.55 (t, 2H, Br-CH₂ -CH₂ -), 3.81 (s, 3H, O-CH₃), 4.56(t, 1H, -CH₂ -CHBr-); C-NMR, decoupled (CDCl₃) 29.60, 36.69, 43.24,53.10, 169.77 ppm. Anal. calcd. for C₅ H₈ O₂ Br₂ (295.934): C, 23.10; H,3.10. Found: C, 23.39; H, 3.14%.

B. N-Methyl-2,4-dibromobutyramide. Methyl 2,4-dibromobutyrate (50 gm,0.192 mole) was mixed with 40 wt % methylamine in aqueous solution (20.0ml, 7.22 gm, 0.232 mole) with stirring and cooling in an ice bath. Thereaction mixture was stirred for 16 hours at 5° C., chloroform (100 ml)was then added and the organic layer washed with water. The organicextract was dried over magnesium sulfate, filtered and the solventremoved. The crude product was purified by column chromatography (silicagel, gradient elution hexane/chloroform to chloroform/ethylacetate) toyield an off-white solid, (25.4 gm, 51.7%): m.p. 42°-47° C. The compoundwas used in the next step without further purification. A small portionwas further purified for elemental analysis; m.p. 48°-49° C. IR(KBr)3450, 1660, 1570, 1415, 1240 and 1210 cm⁻¹ ; H-NMR (CDCl₃) δ2.48 (m, 1H,-CH₂ -CHBr-), 2.79(m, 1H, -CH₂ -CHBy-), (d, 3H, -NH₂ -CH₃ -), 3.55 (t,2H, Br-CH₂ -CH₂), 4.54 (dd, 1H,⁻ CHBr-); 6.39 (s, broad, 1H, -NH-CH₃),C-NMR, decoupled (CDCl₃) 26.83, 30.27, 37.60, 48.26, 168.65 ppm. Anal.calcd. for C₅ H₉ NBr₂ O (258.949): C, 23.19; H, 3.50; N, 5.41. Found: C,23.53; H, 3.44; N, 5.29%.

C. 3-Bromo-N-methyl-2-pyrrolidone. To a stirred solution ofN-methyl-2,4-dibromobutyramide (25.9 gm, 0.1 mole) in 65 ml of dryethanol, kept under nitrogen, was added dropwise an equimolar quantityof freshly prepared sodium ethoxide (2.3 gm Na in 50 ml ethanol) over 40minutes. After two hours the mixture was filtered and the ethanolremoved under reduced pressure. The residue was dissolved in chloroformand washed with water, then washed with saturated aqueous NaCl. Removalof the solvent and distillation under reduced pressure yielded a yellowliquid, (11.55 gm, 65.2%); b.p. 90°-94° C. @ 0.1-1 mm. IR(neat) 1700,1495, 1440, 1405 and 1300 cm⁻¹ ; H-NMR (CDCl₃) δ 2.32 (m, 1H, -CH₂-CHBr-), 2.72 (sextet, 1H, -CH₂ -CHBr-), 2.90 (s, 3H, -N-CH₃), 3.32 (m,1H, N-CH₂ -CH₂ -), 3.58 (m, 1H, N-CH₂ -CH.sub. 2 -), 4.42 (dd, 1H, -CH₂-CHBr-); C-NMR, decoupled (CDCl₃) 33.6, 35.1, 44.2, 47.5, 171.5 ppm.Anal. calcd. for C₅ H₈ BrNO (178.03): C, 33.73; H, 4.53; N, 7.87. Found:C, 33.81; H, 4.52; N, 7.82%.

D. 3-Hydroxy-N-methyl-2-pyrrolidone -3-Bromo-N-methyl-2-pyrrolidone (2.0gm, 0.011 mole) was dissolved in 100 ml of purified water. Potassiumcarbonate (2.33 gm, 0.017 mole) was added while stirring and the mixturewas heated to 100°-110° C. After 4 hours, the reaction mixture waspoured onto ice and neutralized with 1% aqueous HCl. Water was removedunder reduced pressure and the residue extracted with boiling 95%ethanol. After removal of the solvent, the product was purified bycolumn chromatography (silica gel, gradient elution using fromchloroform to chloroform/ethylacetate/methanol) to yield a white solid,(0.754 gm, 58.5%); m.p. 71°-72° C. IR(nujol) 3120(broad), 1670, 1400,1305, 1270 and 1170 cm³¹ 1 ; H-NMR (CDCl₃) δ 1.98 (m, 1H, -CH₂ -CHOH-),2.41 (m, 1H, -CH₂ -CHOH-), 2.84 (s, 3H, -N-CH₃), 3.30 (m, 2H, -CH₂ -N-),4.30 (triplet of doublets, 1H, -CH-OH), 5.18 (d, 1H, -CH-OH), C-NMR,decoupled (CDCl₃) 27.38, -CH₂ -CHOH-), 29.74 (-N-CH₃), 45.74 (-CH₂ -N-),69.41 (-CH-OH-), 175.53 -CHOH-CO-N-) ppm. Partially decoupled and2-dimensional HETCOR spectra support the assignments as given. Anal.calcd. for C₅ H₉ NO₂ (115.129): C, 52.16; H, 7.88; N, 12.17%. Ms(70eV) -Extract molecular ion M⁺ calculated for 115.06332, Found: 115.0634.Fragmentation pattern: 86 (M-29); 54 (M-58); 42 (M-73).

EXAMPLE 2 Radioiodination of 5-chloro-8-hydroxy-iodoquinoline.

This example prepares the radioiodinated control,5-chloro-8-hydroxy-iodoquinoline to be used in tests describedhereinafter to determine the effect of penetration of the3-hydroxy-N-methylpyrrolidone of this invention.

Materials. Sodium Iodide-125 (New England Nuclear NEZ 033, radiochemicaland radionuclidic purity 99%), Sodium iodide-131 (New England NuclearNEZ 035H, radiochemical and radionuclidic purity 99%),5-chloro-8-hydroxy quinoline hydrochloride (Aldrich, lot 3128LJ Cat No.25,044-9), 5-chloro-8-hydroxy-7iodoquinoline (Aldrich, lot 0513KL Cat.No. 22,406-5), Iodobeads (Pierce Chemical Company No. 28666).

Synthesis of 5-chloro-8-hydroxy-7[¹²⁵ I]-Iodoquinoline. An aqueoussolution (0.1N NaOH) containing approximately one mCi of Na¹²⁵ I wasdiluted to 0.5 ml with methanol. Three iodobeads were added and thesolution was left to stand for 5 minutes at room temperature.5-Chloro-8-hydroxyquinoline (0.5 ml of a stock solution containing 200ug/ml in methanol) was added and the reaction vessel was shakenoccasionally for 30 minutes. The iodobeads were then removed,5-chloro-8-hydroxy-7-iodoquinoline (5.0 ml of a stock solutioncontaining 1 mg/ml in methanol) was added followed by 20.0 ml ofpurified water. The resulting white precipitate was filtered and washedwith water until the filtrate activity was at background levels. Theproduct was then dissolved in CH₂ CL₂ (10 ml), transferred to a 25 mlpear shaped flask and the solvent removed under reduced pressure. Assayby uv spectroscopy at 256 nm showed that 4.84 mg of 5-chloro-8-hydroxy-7-iodoquinoline were recovered. Specific activity approximately 120uCi/mg.

Synthesis of 5-chloro-8-hydroxy-7-[¹³¹ I]-Iodoquinoline. This compoundwas prepared by the same procedure described above using Na¹³¹ I.

Assessment of Radiochemical Purity. Analysis and identification ofradiolabeled 5-chloro-8-hydroxy-7-iodoquinoline and determination ofradiochemical purity was performed by HPLC. The HPLC system usedconsisted of the following components: isocratic pump (Altex model 110A,Berkley, Calif.), fixed volume injector (Rheodyne model 7125, Cotari,Calif.), Waters u-Bondapak™ C-18 reverse phase column (Waters Ass.,Milford, Mass.), uv detector (Waters model 440, Milford, Mass.),Radiomatic Model ES stream splitter (Radiomatic Instruments andChemicals, Tampa, Fla.), Radiomatic Model HP flow-through radioactivitydetector (Radiomatic Instruments and Chemicals, Tampa, Fla.), dualchannel strip chart recorder (Linear Instruments Inc., model 858,Irvine, Calif.).

Samples were introduced using a 50ul fixed volume injection loop. Amobile phase containing 70% methanol (Fisher HPLC grade, lot 874675) and30% 0.05M phosphoric acid (Eastman, lot 620) was filtered using a 0.22ufilter, degassed under vacuum and delivered at a flow rate of 1.0ml/min. After passing through the column, the mobile phase effluentpassed through the uv detector set at 254 nm and was split by the streamsplitter. A percentage of the effluent was sent to the flow throughradioactivity detector and the remainder diverted to waste. Thisdetector mixed scintillation coctail (Scintiverse LC, Fisher) with theeffluent in a ratio of 4:1 (v/v). The uv output was recorded on onechannel of the strip chart recorder and the radioactivity output wasrecorded simultaneously on the second channel.

Standards were prepared by dissolving 5.0 mg of unlabeled5-chloro-8-hydroxy-7-iodoquinoline or 5.0 mg of5-chloro-8-hydroxyquinoline in 100 ml of mobile phase to make a finalconcentration of 50 ug/ml. Radioactive samples were prepared bydissolving the reaction product (4.84 mg) in methanol, taking a smallaliquot (100 ul), evaporating and reconstituting in mobile phase.

The retention time for 5-chloro-8-hydroxy-7-iodoquinoline was 10.5minutes. 5-chloro-8-hydroxyquinoline eluted with the solvent front at 3minutes. An HPLC chromatogram for 5-chloro-8-hydroxy-7-[¹³¹I]-iodoquinoline is shown in FIG. 3. In FIG. 3, the upper tracingrepresents UV detection of radioiodination product at 254 nm; A: solventfront/ 5-chloro-8-hydroxyquinoline, B:5-chloro-8-hydroxy-7-iodoquinoline. Lower tracing representsradioactivity detection which was monitored continuously using a flowthrough liquid scintillation counter. Only one radioactive peak (lowertracing) was detected that corresponds to the uv peak of5-chloro-8-hydroxy-7-iodoquinoline.

EXAMPLE 3 In vitro penetration of radioiodinated5-chloro-8-hydroxy-7-iodoquinoline.

General. Standard Franz diffusion cells (15 mm i.d., O-ring design) weremanufactured by Crown Glass Inc., Somerville, N. J. The cell caps weremodified with ground glass joints to fit 14/20 ground glass stoppers. AFranz diffusion cell drive consol F-DCD-9 was also manufactured by CrownGlass. A Vandercamp 2500 recirculating water bath was used to maintainthe cells at 37° C. Split thickness human allograph tissues (0.015 in.thickness), thigh back area, was obtained from the Tissue TransplantBank, St. Agnes Medical Center, Philadelphia, Pa. Samples were countedin a Packard Auto-Gamma Scintillation Spectrometer.

Materials. Sterile Saline (0.9% Sodium Chloride USP, Travenol, NDC0338-0049-04 lot co56747), Albumin (Bovine, fraction v, Sigma A-4503 lot127F-0877), N-Methyl-2-pyrrolidone (Aldrich 99+% Cat No. 24,279-9 lot04402TP), Neomycin Sulfate (Sigma N-1876 lot 66F-0151), absolute ethanol(Midwest Solvents Company of Ill.).

Procedure. Human allograph tissue, which had been stored at -70° C., wasthawed and immediately mounted in a Franz type diffusion cell. Thereceptor chamber was filled with normal saline containing 2% albumin and0.05% neomycin sulfate. Each cell was maintained at 37° C. and stirredat 600 rpm. After the cells had been allowed to equilibrate for 4 to 6hours, 200 ul of a saturated ethanolic solution of5-chloro-8-hydroxy-7-[¹²⁵ I]-iodoquinoline (approx. 70 uCi, 0.44 mg) wasapplied to the donor side of each cell. This was immediately followed byeither 200 μl of absolute ethanol for the control cells, 200 μl of 50%(w/v 3-hydroxy-N-methylpyrrolidone in ethanol or an equimolar ethanolicsolution of N-methylpyrrolidone (43.1% w/v). The cells were then cappedwith ground glass stoppers. At various time intervals, over an 80-100hour period, the entire contents of the receptor chamber was removedwith a 10cc syringe and placed into a vial. The receptor chamber wasthen refilled with fresh solution. After the last collection these vialswere placed in a well-type gamma counter and counted for I-125 activity.

At the time of dosing 200 μl of the saturated 5-chloro-8-hydroxy-7-[¹²⁵I]-iodoquinoline solution was placed into separate vials to calculatethe amount of activity (dose) applied to the skin.

EXAMPLE 4

In this example, 3-hydroxy-N-methyl pyrrolidone was tested for its useas a percutaneous penetration enhancer. In vitro studies were carriedout using Franz type diffusion cells. The penetration enhancingproperties of 3-hydroxy-N-methylpyrrolidone was compared to N-methylpyrrolidone, a compound known to enhance the penetration of drugsthrough the skin.

For these in vitro studies radioiodinated5-chloro-8-hydroxy-7-iodoquinoline was chosen as a model drug. Thisdrug, known as Clioquinol USP, is currently marketed by Ciba (CibaPharmaceutical Company, 556 Morris Avenue, Summit, N. J. 07901), as atopical antibacterial/antifungal agent tradenamed Vioform™. It waschosen because 1) it is a drug that is absorbed very slowly through theskin and 2) Clioquinol inherently has iodine in its structure, allowingeasy preparation of a radiolabeled analogue. This radiolabeled marker isconveniently used to follow the penetration of the drug through theskin.

Franz diffusion cells are designed to mimic in vivo conditions. A finitedose of drug is applied to the stratum corneum side of the skin andpenetration is followed by analyzing for the drug in the receptor phaseunderneath. In these studies the amount of drug crossing the skinbarrier is estimated by counting total radioactivity in the receptorphase. While no excised tissue has been found to duplicate in vivoabsorption in humans, excised human skin is generally regarded as thebest substitute and was therefore used in these studies.

In a preliminary study, the transdermal absorption of Clioquinol wasevaluated in the presence of 3-hydroxy-N-methylpyrrolidone,N-methylpyrrolidone, and in the absence of enhancer. An ethanolicsolution of [I-131]-Clioquinol was applied to 3 cells followed by eitherethanol (control), 50% 3-hydroxy-N-methyl-pyrrolidone in ethanol or anequimolar solution of N-methylpyrrolidone. In FIG. 1, the percentpenetration of 5-chloro-8-hydroxy-7-[¹³¹ I]-iodoquinoline through humanskin is illustrated. The amount of 5-chloro-8-hydroxy-7-[¹³¹I]-iodoquinoline activity applied is equal to 100%. As shown in FIG. 1,the extent of enhancement by 3-hydroxy-N-methyl-pyrrolidone is clearlyevident. At 48.5 hours the amount of I-131 Clioquinol that hadpenetrated through the skin in the presence of3-hydroxy-N-methyl-pyrrolidone (10.2% absorbed) was 3.9 times greaterthan the control (2.6% absorbed) and 1.5 times more than withN-methylpyrrolidone (6.5% absorbed).

The study was repeated using I-125 labeled Clioquinol. Iodine-125 wasused because the longer half-life (t_(1/2) =60d) and lower energy gammaray (0.035 Mev) were better suited to our experimental design. Theresults are shown in FIG. 2. In FIG. 2, the percent penetration of5-chloro-8-hydroxy-7-[¹²⁵ I]-iodoquinoline through the human skin isillustrated. The amount of 5-chloro-8-hydroxy-7[¹²⁵ I]-iodoquinolineapplied is equal to 100%. The relative order of enhancement was found tobe the same with 3-hydroxy-N-methylpyrrolone>N-methylpyrrolone>control.The amount of Clioquinol penetrating the skin in the presence of3-hydroxy-N-methylpyrrolidone (40.0% absorbed) was 1.8 times higher thanthe control (19.5% absorbed) and 1.3 times greater than withN-methyl-pyrrolidone (27.8% absorbed ) at 85.5 hours. Alternatively, thesame amount of Clioquinol was absorbed in approximately 32 hours in thepresence of 3-hydroxy-N-methylpyrrolidone (19% absorbed) as was absorbedin 85 hours in the absence of 3-hydroxy-N-methylpyrrolidone.

The results of these experiments indicate that3-hydroxy-N-methylpyrrolidone shows great potential for use as apercutaneous penetration enhancer. The absorption of Clioquinol wasclearly increased in the presence of 3-hydroxy-N-methylpyrrolidone ascompared to its absorption in the presence of ethanol andN-methylpyrrolidone. In addition, since 3-hydroxy-N-methylpyrrolidone isa major metabolite of N-methylpyrrolidone, it should offer the advantageof being a lower toxicological burden to the body.

The mechanism by which penetration enhancers exert their effects has notbeen clearly established. Possible modes of action that have beensuggested include altering membrane fluidity in the stratum corneum,altering the partitioning behavior of the drug between the stratumcorneum and the underlying dermal tissues and solubilizing the lipidcomponents of the stratum corneum. Most likely penetration enhancerswork by a combination of these and other mechanisms with one mechanismbeing more dominant than others for a particular type of enhancer.Although the mechanism is not known, since 3-hydroxy-N-methylpyrrolidoneeffectively enhances the absorption of a poorly absorbed compound likeClioquinol, this suggests that 3-hydroxy-N-methylpyrrolidone will beeffective for enhancing the percutaneous absorption of many other poorlyabsorbed compounds.

In conclusion, a novel compound, 3-hydroxy-N-methylpyrrolidone, wassynthesized and was shown to effectively enhance the in-vitro absorptionof a model drug. Further, 3-hydroxy-N-methylpyrrolidone is shown to bemore effective than N-methylpyrrolidone in enhancing the absorption ofdrugs. Because it is a metabolite, 3-hydroxy-N-methylpyrrolidone shouldbe metabolically softer to the body and less irritating than othercompounds such as N-methylpyrrolidone. The introduction of a potent,non-toxic and non-irritating compound that can effectively enhance thepenetration of poorly absorbed drugs would open the way for the clinicaluse of transdermal therapeutic systems containing drugs that otherwisecould not be administered by this route.

The invention has been described herein with reference to certainpreferred embodiments. However, as obvious variations thereon willbecome apparent to those skilled in the art, the invention is not to beconsidered as limited thereto.

We claim:
 1. An article of manufacture for the continuous administrationof drugs by absorption through the skin which comprises as a penetrationenhancer for the drug, 3-hydroxy-N-methylpyrrolidone.
 2. An article ofmanufacture according to claim 1 wherein the article of manufacturecomprises a reservoir for the drug and the penetration enhancer, abacking member, and a pressure-sensitive adhesive for application of thearticle to the skin.
 3. A method for the administration of drugs throughthe human skin which comprises preparation of a drug delivery systemwhich contains the drug and as a penetration enhancer,3-hydroxy-N-methylpyrrolidone, and applying the composition to the humanskin.